This invention relates to the recovery of natural fluids from subterranean reservoirs. More particularly, this invention relates to a process for recovering hydrocarbons from hydrocarbon-bearing formations. More specifically, this invention relates to post primary hydrocarbon recovery processes in which the formation is first treated with a sacrificial agent followed by injection of microbial agents.
The production of petroleum products is usually accomplished by drilling into a hydrocarbon bearing formation and utilizing one of the well known recovery methods for the recovery of hydrocarbons. However, it is recognized that these primary recovery techniques may recover only a minor portion of the petroleum present in the formation particularly when applied to reservoirs of viscous crudes. Even the use of improved recovery practices involving steam, surfactantflooding, waterflooding and polymerflooding can result in up to 50-60 percent of the original hydrocarbons being left in place.
Thus, many large reserves of petroleum fluids from which only small recoveries have been realized by present commercial recovery methods remain in place.
It is known that bacteria can be introduced into subterranean formations for the purpose of beneficially influencing the factors which control the quantity of valuable fluids which can be recovered from the formations or which control the facility with which such fluids are recoverable. Microbial cells have a strong surface charge and, therefore, are readily adsorbed by the rock surface and clay particles in porous media. Consequently, microbial cells are very difficult to transport through porous media because the microorganisms are readily adsorbed on the reservoir rock.
The positive but indirect manner by which in-situ bacterial cell metabolism enhances oil recovery depends on the successful positioning of such cells deep in the oil bearing formation. Once in position, cell metabolism can give rise, e.g., to gas production such as CO.sub.2 or surfactant production such as carboxylic acids which can be beneficial to enhanced oil recovery operations. The positioning of bacterial cells in subterranean rock strata is hindered by the natural tendency of such cells to be strongly adsorbed on the rock surface. This adsorption prevents the facile injection of the cells and severe plugging of the rock matrix results at a short distance from the injection site. The present invention proposes the use of known sacrificial agents to facilitate the injection and thus the successful positioning of bacterial cells deep in the rock strata, i.e., at a great distance from the site of bacterial cell injection. It is contemplated that the sacrificial agent, usually as an aqueous solution, can be injected prior to the injection of the bacterial cells or simultaneously with the bacterial cells.
The general use of sacrificial agents in the prior art to diminish the adsorption of subsequently or simultaneously injected surfactants and/or polymers in enhanced oil recovery operations is disclosed, e.g., in patents such as U.S. Pat. Nos. 3,532,166; 3,469,630; 3,478,823; 4,157,115; 4,217,958; 3,804,173; 4,005,749; 4,207,946; 3,797,574 and 3,778,399. These patents encompass a variety of sacrificial agents such as alkali metal carbonates and polyphosphates; low molecular weight water soluble polymeric viscosifiers; lignosulfonates and polybasic carboxylic acids. The use of these agents for the facilitation of bacterial cell injection into subterranean rock strata does not appear to be disclosed in the prior art.
Since it is recognized that significant amounts of surfactant and/or polymer are "lost" by rock adsorption in enhanced oil recovery operations, it is contemplated that such previously surfactantflooded and/or polymerflooded reservoirs are amenable to bacterial cell injection because a significant proportion of the rock adsorption sites would be occupied by surfactant and/or polymeric species. This adsorption gradient would be expected to facilitate the in depth penetration of the subsequently injected bacterial cells.
Accordingly, an object of this invention is to provide an improved process for the recovery of oil from subterranean oil reservoirs.
A further object of this invention is to provide an improved process for the post-primary or enhanced recovery of oil from subterranean formations.
A further object of this invention is to provide an improved process for the utilization of microbial cells in recovery of hydrocarbons from subterranean formations.
Other objects, aspects, as well as the several advantages of the invention will be apparent to those skilled in the art upon reading the specification and the appended claims.